Macrocapsules containing microencapsulated phase change materials

ABSTRACT

The present invention is directed to a method for producing macrocapsules containing therein a plurality of microcapsules. In accordance with some embodiments of the present invention, the microcapsules contain a phase change material.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application is a divisional of application Ser. No.09/964,777, filed Sep. 27, 2001, which claims the benefit of U.S.provisional application Serial No. 60/235,850, filed Sep. 27, 2000.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to thermal energy storagecompositions comprising macrocapsules or beads containing phase changematerials (PCMs) and, more particularly, to macrocapsules containingmicroencapsulated phase change materials. Although the focus of thepresent application is directed to encapsulation of phase changematerials, the procedure described herein can also be used toencapsulate a variety of materials, such as fragrances, pharmaceuticals,pesticides, oils, lubricants, and the like.

[0003] U.S. Pat. No. 5,415,222 to Colvin, et al. discloses a coolinggarment, preferably in the form of a vest that contains pouchescontaining a phase change material. In one embodiment the coolinggarment includes a honeycomb structure which is contained within thepouches and which contains a macroencapsulated phase change material andallows the escape of perspiration through the garment. The coolinggarments are designed to permit evaporative cooling to occur and tocontribute to the overall comfort of the wearer.

[0004] U.S. Pat. No. 5,290,904 to Colvin, et al. discloses a thermalshield which may include a phase change material in bulk, micro or macroencapsulated to provide enhanced thermal protection.

[0005] U.S. Pat. No. 4,911,232 to Colvin, et al. and U.S. Pat. No.5,007,478 to Sengupta disclose the use of slurries of microencapsulatedPCMs in thermal loops for heat transfer in systems which necessitate theuse of more efficient thermal transfer fluids, such as systems in whichlarge quantities of heat must be removed in short periods of time orsystems in which there are system size restrictions which limit thevolume of fluid which can be transported in the thermal loop. Suchsystems include lasers, electronic components, supercomputers, nucleargenerators, etc.

[0006] U.S. Pat. No. 4,756,958 to Bryant discloses fibers and fabricswhich incorporate microencapsulated PCMs. These materials exhibitenhanced thermal energy storage properties and can be manufactured intogarments useful in extreme cold or extreme heat.

[0007] U.S. Pat. No. 4,513,053 discloses microencapsulating PCMs forincorporation into concrete or plastics.

[0008] The disclosures of the above-identified patents are incorporatedherein by reference.

SUMMARY OF THE INVENTION

[0009] The present invention is directed to thermal energy storagecompositions comprising macrocapsules containing therein a plurality ofmicrocapsules and to methods for producing macrocapsules containingmicrocapsules. In accordance with some embodiments of the presentinvention, the microcapsules contain a phase change material.

[0010] In accordance with one embodiment of the present invention, amethod for producing a macrocapsule containing a plurality ofmicrocapsules therein comprises the steps of providing a plurality ofmicrocapsules; suspending the plurality of microcapsules in a gellingagent solution thereby forming a suspension of microcapsules in thegelling agent. Suspension of adding the microcapsules as discrete dropsto a crosslinking solution thereby crosslinking the gelling agentcoating and forming discrete macrocapsules, and drying themacrocapsules.

[0011] Macrocapsules prepared in accordance with the present inventioncan be incorporated inside a coat, vest or other article for the purposeof absorbing body heat to increase the wearer's comfort level and thusto increase the length of time that the wearer can engage in a physicalactivity. The macroencapsulated phase change materials can be used in avariety of products such as firefighting garments, hazmat suits,specialized clothing for foundry workers, armed forces, etc.

[0012] The macrocapsules of the present invention may be used in anyapplication relating to the transfer and/or storage of heat. Specificexamples include, but are not limited to, the use of these materials inHVAC systems and construction materials for residential and commercialbuildings, home furnishings and automobile upholstery, heat sinks forcomputers, etc.

[0013] The macrocapsules of the invention have a particle size in therange of 1000 to 10,000 microns with a PCM payload of at least 50%, moreparticularly at least 75% and in accordance with some embodiments atleast 80%. Conventional type microcapsules in this size range based onthe reservoir type core concept present production problems. Theseproblems in production are obviated by macroencapsulating highconcentrations of microencapsulated PCMs.

[0014] In accordance with the present invention, microcapsulescontaining PCMs are added to a gelling solution and mixed thoroughly.After mixing, the gel/microcapsule mixture is dripped into acrosslinking solution to form discrete gel droplets. The droplets areremoved from the crosslinking solution, rinsed with water and dried to aconsistency of less than 1% moisture to produce macrocapsules accordingto the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention is directed to thermal energy storagecompositions comprising macrocapsules containing therein a plurality ofmicrocapsules. In accordance with some embodiments of the presentinvention, the microcapsules contain a phase change material. Byencapsulating microcapsules having a high payload of phase changematerial in larger macrocapsules, it is possible to produce thermalenergy storage compositions having a relatively high payload of phasechange material in the finished composition. Macrocapsules prepared inaccordance with the present invention comprise a wall material formed byadding a slurry of microcapsules suspended in a gelling agent to acrosslinking solution wherein the crosslinking composition crosslinksthe gel to form discrete gel droplets containing a plurality ofmicrocapsules. The discrete gel droplets are separated from thecrosslinking solution, rinsed with water and dried to a consistency ofless than 1% moisture. The resulting thermal energy storage material maybe incorporated into a number of articles including building materials,food serving trays, medical wraps, clothing or any applications wherethermal energy storage materials are conventionally used.

[0016] Any of a variety of processes known in the art may be used tomicroencapsulate PCMs in accordance with the present invention. One ofthe most typical methods which may be used to microencapsulate a PCM isto disperse droplets of the molten PCM in an aqueous solution and toform walls around the droplets using techniques such as coacervation,interfacial polymerization and in situ polymerization all of which arewell known in the art. For example, the methods are well known in theart to form gelatin capsules by coacervation, polyurethane or polyureacapsules by interfacial polymerization, and urea-formaldehyde,urea-resorcinol-formaldehyde, and melamine formaldehyde capsules by insitu polymerization. In accordance with particular embodiments of thepresent invention, the wall material for encapsulating PCMs ismelamine-formaldehyde.

[0017] Generally speaking, phase change materials have the capability ofabsorbing or releasing thermal energy to reduce or eliminate heattransfer at the temperature stabilizing range of the particulartemperature stabilizing material. The phase change material inhibits orstops the flow of thermal energy through the material during the timethe phase change material is absorbing or releasing heat, typicallyduring the material's change of phase. This action is transient, i.e.,it will be effective as a barrier to thermal energy until the totallatent heat of the temperature stabilizing materials is absorbed orreleased during the heating or cooling process. Thermal energy may bestored or removed from the phase change material, and can effectively berecharged by a source of heat or cold. Two or more different phasechange materials can be used to address particular temperature rangesand such materials can be mixed.

[0018] PCMs useful in the invention include paraffinic hydrocarbonshaving 13 to 28 carbon atoms. For example, the melting point of ahomologous series of paraffin hydrocarbons is directly related to thenumber of carbon atoms as shown in the following table: Compound NameNumber of Carbon Atoms Melting Point (° C.) n-Octacosane 28 61.4n-Heptacosane 27 59.0 n-Hexacosane 26 56.4 n-Pentacosane 25 53.7n-Tetracosane 24 50.9 n-Tricosane 23 47.6 n-Docosane 22 44.4n-Heneicosane 21 40.5 n-Eicosane 20 36.8 n-Nonadecane 19 32.1n-Octadecane 18 28.2 n-Heptadecane 17 22.0 n-Hexadecane 16 18.2n-Pentadecane 15 10.0 n-Tetradecane 14 5.9 n-Tridecane 13 −5.5

[0019] Additionally, crystalline materials such as 2,2-dimethyl-1,3-propanediol, 2-hydroxymethyl-2-methyl-1, 3-propanediol, acids ofstraight or branched chain hydrocarbons such as eicosanoic acid andesters such as methyl palmitate, and fatty alcohols may be used as PCMsin the present invention. In fact, substantially any hydrophobic PCMwhich can be dispersed in water and microencapsulated by the technologyreferenced above may be useful in the present invention. Microcapsulescontaining octadecane are utilized in accordance with particularembodiments of the present invention.

[0020] The size of the microcapsules typically range from about 1 to 100microns and more typically from about 2 to 50 microns. The capsule sizeselected will depend on the application in which the microencapsulatedPCM is used. For use in heat transfer fluids, the capsule size may rangefrom about 1 to 100 microns and more typically from about 2 to 40microns.

[0021] The microcapsules will typically have a relatively high payloadof phase change material, typically at least 70% by weight, moretypically at least 80% by weight, and in accordance with someembodiments, the microcapsules may contain more than 90% phase changematerial.

[0022] Gelling agents useful in the present invention includepolysaccharides, nonionic polymers, inorganic polymers, polyanions andpolycations. Examples of polysaccharides useful in the present inventioninclude, but are not limited to, alginate and natural ionicpolysaccharides such as chitosan, gellan gum, xanthan gum, hyaluronicacid, heparin, pectin and carrageenan. Examples of ionicallycrosslinkable polyanions suitable for use in the practice of the presentinvention include, but are not limited to, polyacrylic acid andpolymethacrylic acid. Ionically crosslinkable polycations such aspolyethylene imine and polylysine are also suitable for use in thepresent invention. A specific example of a non-ionic polymer ispolyvinylalcohol. Sodium silicates are examples of useful inorganicpolymers.

[0023] The gelling agents are typically provided as an aqueous solutionat a concentration and viscosity sufficient to provide the desiredamount of coating on the microcapsules. The technology ofmacroencapsulation is known to those skilled in the art as is theroutine optimization of these parameters for the gelling agent.

[0024] In accordance with one embodiment of the present invention,polysaccharide alginate serves as the gelling agent. Alginate as usedherein refers to salts of alginic acid. A preferred alginate ismanufactured by Grindsted, Inc. and is available commercially under theTradename SOBALG-FD 120.

[0025] Preferrably, the alginate is provided in a concentration range of1% to 15% by weight. It should be appreciated, however, that varyingamounts or concentration ranges of alginates in the final mixture may beutilized in order to carry out the invention.

[0026] The crosslinking solution typically comprises a material capableof crosslinking the gelling agent to form a crosslinked gelling agent.Typical crosslinking materials include multivalent ions, in particularcations. Cations useful in crosslinking the gelling agent includemagnesium, calcium, zinc, barium, strontium, aluminum, iron, manganese,nickel, cobalt, copper, cadmium, lead, or mixtures of any 2 or morethereof. Calcium, barium, and strontium are useful in particularembodiments, with calcium being a particularly useful cation forcrosslinking the gelling agent of the mixture. Calcium chloride isparticularly useful and is available commercially from AmbarManufacturing Co. The cationic crosslinking agent is used in an amountsufficient to crosslink the gelling agent as is known in the art.

[0027] Macrocapsules containing a plurality of microcapsules inaccordance with the present invention are produced by providing aplurality of microcapsules; suspending the plurality of microcapsules ina gelling agent solution thereby forming a suspension of microcapsulesin the gelling agent; adding the suspension of microcapsules as dropletsof a desired size to a crosslinking solution thereby crosslinking thegelling agent around the microcapsules and forming discretemacrocapsules wherein each macrocapsule contains a plurality ofmicrocapsules; removing the formed macrocapsules from the crosslinkingsolutions; rinsing the macrocapsules with water and drying to aconsistency of less than 1% moisture.

[0028] Macrocapsules prepared in accordance with the present inventioncan range in particle size from 1000 to 10,000 microns with a PCMloading of at least 50%, more particularly at least 75%, and in someembodiments at least 80% weight.

[0029] The following non-limiting examples illustrate the preparation ofmacrocapsules in accordance with the present invention.

EXAMPLE 1

[0030] 1) 10% alginate solution

[0031] Feather in 2.5 grams alginate into 22.5 grams of water whileagitating with a lab stir motor equipped with a turbine blade.

[0032] 2) 10% calcium chloride solution

[0033] Add 120 grams calcium chloride to 1080 grams water. Stir thissolution to dissolve the calcium chloride using a laboratory stir motorequipped with a turbine blade.

[0034] 3) Microcapsule slurry

[0035] PCM microcapsules 10-40μ, 88% payload (octadecane) commerciallyavailable from Microtek. Add 25 grams of dry microcapsules containingoctadecane at an 88% core content to 75 ml deionized water. Stir themixture using the stir motor/blade to thoroughly mix the components sothat no lumps of the microcapsules are remaining.

[0036] 4) Thoroughly mix the microcapsule slurry with the 10% alginatesolution.

[0037] 5) Slowly drip in the alginate/microcapsule mixture into thecalcium chloride solution using a dropping funnel to regulate the flowof the alginate/microcapsule mixture. Slowly agitate the calciumchloride solution using a stir motor/blade to keep the droplets fromagglomerating.

[0038] 6) Remove the gelled droplets from the calcium chloride solution,rinse with water and dry in an oven to a dryness of <1% moisture.

[0039] The size of the finished product is an average of 3440 microns.The moisture content was 0.88%. The theoretical wax content of theparticles was approximately 75 to 80%.

[0040] Calcium oxide dissolved in a solution of hydrochloric acid willalso be effective as a crosslinking salt solution. The microencapsulatedphase change material can be added as a wet cake instead of as a drypowder. Several other concentrations of alginate, calcium chloride andmicrocapsules can be utilized. The size of the microencapsulated phasechange material can also be varied as well as the PCM content.

EXAMPLE 2

[0041] Polyvinyl Alcohol—Sodium Tetraborate System

[0042] Solution #1—15 grams sodium tetra borate dissolved in 300 ml DIwater (the solution was saturated with some undissolved borate)

[0043] Solutions #2—3 grams polyvinyl alcohol (PVA) dissolved in 27 mlDI water (10% solution) Grade 540 from Air Products Company

[0044] 54.1 grams of wet cake (53.9% solids) of microencapsulated PCMwax.

[0045] Thoroughly mixed the microcapsules with the solution 1 anddripped the resulting slurry into solution 2 that was agitated using avariable speed stir motor and turbine. The resulting rubbery beads wereremoved from the solution 1 container and allowed to dry overnight. Someof the resulting soft beads were placed into a beaker containingisopropyl alcohol to enhance the drying of the large droplets. Thedroplets from the isopropyl alcohol were then also dried overnight.

EXAMPLE 3

[0046] Sodium Silicate

[0047] 50 Grams Silicate of Soda (˜57% Solids) obtained from ChemServices and 50 grams of a water wet filter cake containing about 60% byweight microencapsulated technical grade Octadecane were mixed well.Using a disposable pipette, the mixture was dripped a drop at a time,into a saturated solution of magnesium sulfate (Epsom Salts) with slowagitation. Beads of approximately 3 to 4 mm in diameter were formed assoon as the droplets entered the salt solution. They were isolated byfiltering and dried on the bench top. The round beads thus formedcontained about 50% technical grade Octadecane.

EXAMPLE 4

[0048] Gelatin Gluteraldehyde—Alum System

[0049] 10 grams of 300 Bloom pork skin gelatin were dissolved in 90grams of deionized water using agitation and heat in a 150 ml beaker. 10grams of the solution were removed to which 5 grams of water and 10grams of microencapsulated PCM were added. The resulting slurry wasstirred until well dispersed. 100 ml of saturated alum (aluminumsulfate) solution were poured into a 400 ml beaker and 2 grams of 50%gluteraldehyde solution were added, with agitation. Continued theagitation and added drop-wise the gelatin slurry to the alum solution,thus forming large droplets that can be dried to form hard beads(macrocapsules) containing microencapsulated phase change material.

What is claimed is:
 1. A method for producing macrocapsules containing aplurality of microcapsules therein, said method comprising: a. providinga plurality of microcapsules; b. suspending said plurality ofmicrocapsules in a gelling agent solution thereby forming a suspensionof said microcapsules in said gelling agent solution; c. adding saidsuspension of microcapsules as discrete drops to a crosslinking solutionthereby crosslinking said gelling agent coating and forming discretemacrocapsules wherein each macrocapsule contains a plurality ofmicrocapsules; and d. drying said macrocapsules.
 2. A method forproducing macrocapsules in accordance with claim 1 wherein saidmicrocapsules contain a phase change material.
 3. A method for producingmacrocapsules in accordance with claim 2 wherein said phase changematerial is selected from the group consisting of: n-Octacosane,n-Heptacosane, n-Hexacosane, n-Pentocosane, n-Tetracosane, n-Tricosane,n-Docosane, n-Homeiocosane, n-Eicosane, n-Nonadecane, n-Octadecane,n-Heptadecane, n-Hexadecane, n-Pentadecane, n-Tetradecane andn-Tridecane.
 4. A method for producing macrocapsules in accordance withclaim 1 wherein said macrocapsules have an average particle size of 1000to 10,000 microns.
 5. A method for producing macrocapsules in accordancewith claim 1 wherein said gelling agent is selected from the groupconsisting of polysaccharides, nonionic polymers, inorganic polymers,polyanions and polycations.
 6. A method for producing macrocapsules inaccordance with claim 5 wherein said gelling agent is alginate.
 7. Amethod for producing macrocapsules in accordance with claim 1 whereinsaid crosslinking solution comprises cations selected from the groupconsisting of sodium, magnesium, calcium, zinc, barium, strontium,aluminum, iron, manganese, nickel, cobalt, copper, cadium, lead, andmixtures thereof.
 8. The method for producing microcapsules inaccordance with claim 2 wherein said macrocapsules have a payload of atleast 50% phase change material by weight.
 9. The method for producingmicrocapsules in accordance with claim 8 wherein said macrocapsules havea payload of at least 75% phase change material by weight.
 10. Themethod for producing microcapsules in accordance with claim 9 whereinsaid macrocapsules have a payload of at least 80% phase change materialby weight.
 11. The method for producing microcapsules in accordance withclaim 10 wherein said macrocapsules have a particle size of from about1000 to 10,000 microns.
 12. The method for producing microcapsules inaccordance with claim 3 wherein said phase change material comprisesn-Octadecane.
 13. The method for producing microcapsules in accordancewith claim 1 wherein said microcapsules have an average particle size offrom about 2 to 50 microns.
 14. The method for producing microcapsulesin accordance with claim 1 wherein said gelling agent is selected fromthe group consisting of alginate, polyvinyl alcohol, sodium silicate andgelatin.